This project seeks to characterize the enduring and temporary physiological and behavioral developmental differences among animals born during different seasons of the year, with emphasis on how young animals determine the season of the year and the par- ticular role of the mother in communicating seasonal information. Specific projects include: 1) determining the role of Pre- and postnatal photoperiod on physiological and behavioral development; 2) determining the role of maternal melatonin on development of her offspring; 3) assessing the role of other, non-melatonin factors affected by photoperiod in the mother that in turn influence pup development; 4) determining whether pups born in photoperiods typical of various seasons of the year respond differently to a standard photoperiod postnatally; 5) assessing the functional significance of differences in pup development in litters born to mothers simulating breeders from various seasons of the year; 6) determining the significance and permanence of early fur growth in pups born to mothers housed in winter photoperiods. The proposed work may lead to concepts and interventions that could provide insight into how season of birth alters the incidence of schizophrenia, alcoholism and growth pattern in the human population.